From: Dave Hansen <dave.hansen@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Rik van Riel <riel@redhat.com>,
daniel.gruss@iaik.tugraz.at, hughd@google.com,
keescook@google.com, linux-mm@kvack.org,
michael.schwarz@iaik.tugraz.at, moritz.lipp@iaik.tugraz.at,
richard.fellner@student.tugraz.at
Subject: Re: [patch V2 1/5] x86/kaiser: Respect disabled CPU features
Date: Mon, 27 Nov 2017 10:11:12 -0800 [thread overview]
Message-ID: <07d101b3-d17a-7781-f05e-96738e6d6848@linux.intel.com> (raw)
In-Reply-To: <20171126232414.313869499@linutronix.de>
> --- a/arch/x86/include/asm/pgtable_64.h
> +++ b/arch/x86/include/asm/pgtable_64.h
> @@ -222,7 +222,8 @@ static inline pgd_t kaiser_set_shadow_pg
> * wrong CR3 value, userspace will crash
> * instead of running.
> */
> - pgd.pgd |= _PAGE_NX;
> + if (__supported_pte_mask & _PAGE_NX)
> + pgd.pgd |= _PAGE_NX;
> }
Thanks for catching that. It's definitely a bug. Although,
practically, it's hard to hit, right? I think everything 64-bit
supports NX unless the hypervisor disabled it or something.
> } else if (pgd_userspace_access(*pgdp)) {
> /*
> --- a/arch/x86/mm/kaiser.c
> +++ b/arch/x86/mm/kaiser.c
> @@ -42,6 +42,8 @@
>
> #define KAISER_WALK_ATOMIC 0x1
>
> +static pteval_t kaiser_pte_mask __ro_after_init = ~(_PAGE_NX | _PAGE_GLOBAL);
Do we need a comment on this, like:
/*
* The NX and GLOBAL bits are not supported on all CPUs.
* We will add them back to this mask at runtime in
* kaiser_init_all_pgds() if supported.
*/
> /*
> * At runtime, the only things we map are some things for CPU
> * hotplug, and stacks for new processes. No two CPUs will ever
> @@ -244,11 +246,14 @@ static pte_t *kaiser_shadow_pagetable_wa
> int kaiser_add_user_map(const void *__start_addr, unsigned long size,
> unsigned long flags)
> {
> - pte_t *pte;
> unsigned long start_addr = (unsigned long)__start_addr;
> unsigned long address = start_addr & PAGE_MASK;
> unsigned long end_addr = PAGE_ALIGN(start_addr + size);
> unsigned long target_address;
> + pte_t *pte;
> +
> + /* Clear not supported bits */
> + flags &= kaiser_pte_mask;
Should we be warning on these if we clear them? Seems kinda funky to
silently fix them up.
> for (; address < end_addr; address += PAGE_SIZE) {
> target_address = get_pa_from_kernel_map(address);
> @@ -308,6 +313,11 @@ static void __init kaiser_init_all_pgds(
> pgd_t *pgd;
> int i;
>
> + if (__supported_pte_mask & _PAGE_NX)
> + kaiser_pte_mask |= _PAGE_NX;
> + if (boot_cpu_has(X86_FEATURE_PGE))
> + kaiser_pte_mask |= _PAGE_GLOBAL;
Practically, I guess boot_cpu_has(X86_FEATURE_PGE) == (cr4_read() &
X86_CR4_PGE). But, in a slow path like this, is it perhaps better to
just be checking CR4 directly?
Looks functionally fine to me, though. Feel free to add my Reviewed-by
or Acked-by.
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next prev parent reply other threads:[~2017-11-27 18:11 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-26 23:14 [patch V2 0/5] x86/kaiser: Boot time disabling and debug support Thomas Gleixner
2017-11-26 23:14 ` [patch V2 1/5] x86/kaiser: Respect disabled CPU features Thomas Gleixner
2017-11-27 9:57 ` Peter Zijlstra
2017-11-27 11:47 ` Thomas Gleixner
2017-11-27 12:31 ` Brian Gerst
2017-11-27 13:18 ` Thomas Gleixner
2017-11-27 18:11 ` Dave Hansen [this message]
2017-11-27 18:37 ` Kees Cook
2017-11-26 23:14 ` [patch V2 2/5] x86/kaiser: Simplify disabling of global pages Thomas Gleixner
2017-11-27 11:49 ` Thomas Gleixner
2017-11-27 18:15 ` Dave Hansen
2017-11-27 20:28 ` Thomas Gleixner
2017-11-26 23:14 ` [patch V2 3/5] x86/dump_pagetables: Check KAISER shadow page table for WX pages Thomas Gleixner
2017-11-27 18:17 ` Dave Hansen
2017-11-26 23:14 ` [patch V2 4/5] x86/mm/debug_pagetables: Allow dumping current pagetables Thomas Gleixner
2017-11-27 9:41 ` Peter Zijlstra
2017-11-27 10:06 ` [PATCH] vfs: Add PERM_* symbolic helpers for common file mode/permissions Ingo Molnar
2017-11-27 19:21 ` Linus Torvalds
2017-11-28 10:54 ` Ingo Molnar
2017-11-28 11:12 ` Ingo Molnar
2017-11-29 8:52 ` Michael Ellerman
2017-11-27 18:18 ` [patch V2 4/5] x86/mm/debug_pagetables: Allow dumping current pagetables Dave Hansen
2017-11-26 23:14 ` [patch V2 5/5] x86/kaiser: Add boottime disable switch Thomas Gleixner
2017-11-27 9:48 ` Peter Zijlstra
2017-11-27 10:22 ` Peter Zijlstra
2017-11-27 11:50 ` Thomas Gleixner
2017-11-27 12:49 ` Peter Zijlstra
2017-11-27 21:43 ` Peter Zijlstra
2017-11-27 18:22 ` Dave Hansen
2017-11-27 19:00 ` Thomas Gleixner
2017-11-27 19:18 ` Josh Poimboeuf
2017-11-27 20:47 ` Thomas Gleixner
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